Heretofore, lubricating oil is used in driving apparatuses and gears in internal combustion engines, automatic transmissions, dampers, and power steering gears for achieving smooth movement. However, it is known that the lubricating property is insufficient when the apparatuses and gears are used for achieving a high output under a large load. The surface of lubrication is worn out by friction, and seizure finally takes place. Therefore, lubricating oil containing an extreme pressure agent or a wear inhibitor is used. However, conventional extreme pressure agents have problems in that a sufficient effect for preventing seizure is not exhibited because of interaction with other additives, metals are corroded, and wear resistance is inferior, and are not always satisfactory.
As for oil used for metal working, such as cutting, grinding, and deformation processing, improvement in workability has been attempted by adding various types of oiliness improver or extreme pressure agent to mineral oil or synthetic hydrocarbon oil. For example, metal working oils prepared by adding an extreme pressure agent containing sulfur or chlorine to a base oil are commercially available. However, these metal working oils are not always satisfactory with respect to the life of tools and the efficiency of working represented by the precision of a finished surface of a processed material.
Therefore, development of an additive which exhibits the function of improving efficiency of working and decreasing wear of tools by forming a stronger lubricating film has been desired.
Moreover, when a working oil contains a large amount of an extreme pressure agent containing chlorine, there is the possibility that compounds causing environmental hazard (chlorine gas, dioxine, and the like) are formed when waste oil is disposed. Moreover, even when an extreme pressure agent containing sulfur is used, there is the possibility that environmental hazard is caused by the formation of SO.sub.x gas. Therefore, development of an extreme pressure agent which does not cause environmental hazard and has excellent properties has been desired.
A hydraulic fluid is a power transmission fluid which is used for transmission of power, control of force, and buffering in hydraulic systems, such as hydraulic devices and apparatuses, and also has the function of lubrication of sliding parts.
For such a hydraulic fluid, it is essential that the fluid has an excellent resistance to seizure under load and wear resistance as the fundamental properties. Therefore, these properties are provided by addition of an extreme pressure agent and a wear inhibitor to a base oil, such as mineral oil or synthetic oil. However, conventional extreme pressure agents are not always satisfactory in that the wear resistance is insufficient or corrosive wear takes place although the effect of preventing seizure under load is sufficiently exhibited.
For a hydraulic fluid, such as a fluid for traction drive, a relatively high friction coefficient is required in addition to the lubricating property. Therefore, development of an additive which can provide such a property (a friction coefficient modifier) has been desired.
On the other hand, the industry in Japan is placed under various regulations of the Fire Services Act for prevention of fire. For example, many types of lubricating oil are classified as the fourth grade hazardous material and the method of handling in accordance with the place of handling is strictly regulated. It is recommended by the fire department that fire-retarded lubricating oil is used in buildings.
As the fire-retarded lubricating oil, for example, lubricating oils containing a halogen, such as lubricating oils containing chlorine and lubricating oils containing fluorine, lubricating oils containing an ester of phosphoric acid, lubricating oils containing an ester of a fatty acid, and lubricating oils containing water have been developed. Among these lubricating oils, some of the lubricating oils containing a halogen and the lubricating oils containing water show no flash point in the measurement of the flash point of the fourth grade hazardous materials in accordance with the Fire Services Act of Japan. Therefore, these lubricating oils are non-hazardous materials which are not regulated by the Fire Services Act. Particularly, the demand for the lubricating oils containing water has been increasing because these oils show a high degree of safety against fire, and additional equipments for complying with the regulation are not necessary.
However, among the lubricating oils which are classified as the non-hazardous material, the lubricating oils containing chlorine have drawbacks in that the lubricating oils cause corrosion of metals to a great degree, are easily decomposed, form toxic gases by decomposition, and therefore, require careful handling. The lubricating oils containing fluorine are very expensive although these oils are much more stable than the lubricating oils containing chlorine. Therefore, the application of these oils is inevitably limited, and these oils are used only for special applications.
The lubricating oils containing water can generally be classified into W/O oils of the emulsion type (the emulsion type and the solution type), O/W oils of the emulsion type, and water-glycol oils. The problem common to these lubricating oils is an insufficient lubricating property and vaporization of water. Because these lubricating oils contain water, the lubricating property is inevitably inferior. When water is lost by vaporization, the fire-retardant property is also lost, and the oils become hazardous materials having a flash point. Therefore, the content of water must be controlled, and this requires additional man power and cost.
Moreover, a surfactant or a glycol is used so that the oil can contain water. Such an additive shows an adverse effect to sealing materials and coating materials. A lubricating oil of the water-glycol type causes a higher COD (chemical oxygen demand) in the waste water, and there is the possibility of causing an adverse effect to the environment. Therefore, this lubricating oil has a drawback in that a great cost is required for treatment of waste water.